The PowerPoint briefing, titled "A History of Concealment and Deception," has been presented to diplomats from more than a dozen countries. Several diplomats said the presentation, intended to win allies for increasing pressure on the Iranian government, dismisses ambiguities in the evidence about Iran's intentions and omits alternative explanations under debate among intelligence analysts.

The presenters argue that the evidence leads solidly to a conclusion that Iran's nuclear program is aimed at producing weapons, according to diplomats who have attended the briefings and U.S. officials who helped to assemble the slide show. But even U.S. intelligence estimates acknowledge that other possibilities are plausible, though unverified.

The problem, acknowledged one U.S. official, is that the evidence is not definitive. Briefers "say you can't draw any other conclusion, and of course you can draw other conclusions," said the official, who would discuss the closed-door sessions only on condition of anonymity.

The briefings were conducted in Vienna over the past month in advance of a gathering of world leaders this week at the United Nations. President Bush, who is to address the annual General Assembly gathering Wednesday, and Secretary of State Condoleezza Rice, plan to use the meeting to press for agreement to threaten international sanctions against Iran.

The president's direct involvement marks an escalation of a two-year effort to bring Iran before the U.N. Security Council, which has the power to impose sanctions, unless Tehran gives up technology capable of enriching uranium for a bomb. U.S. officials have acknowledged that it has been an uphill campaign, with opposition from key allies who fear a prelude to a military campaign.

Several diplomats said the slide show reminded them of the flawed presentation on Iraq's weapons programs made by then-secretary of state Colin L. Powell to the U.N. Security Council in February 2003. "I don't think they'll lose any support, but it isn't going to win anyone either," said one European diplomat who attended the recent briefing and whose country backs the U.S. position on Iran.

Robert G. Joseph, undersecretary of state for arms control and international security, acknowledged last week that despite European support, the Bush administration has traveled a tough road in persuading others that Iran should face consequences for a nuclear program it built in secret.

"There's a great deal of resistance . . . on the part of many governments who don't seem to place, quite frankly, nonproliferation and Iran, a nuclear-armed Iran, at the top of their priority list," he told a congressional panel last week.

Several influential nations such as India, Russia, China, South Africa and Brazil share U.S. suspicions about Iran's intentions. But they maintain profound differences with the Bush administration over how to respond, and are apprehensive about the goals of a U.S. president who has said "all options are on the table," in dealing with Tehran.

Three years ago, the White House used the same annual gathering to put both Iraq, and the world community on notice. In a toughly-worded speech, delivered six months before the U.S. invasion of Iraq, Bush warned that the United States would deal alone, if necessary, with a dictator bent on launching nuclear weapons.

The U.S. intelligence community no longer believes Iraq was trying to reconstitute a nuclear program, as the president said. Those and other U.S. intelligence failures have remained fresh in the minds of international decision-makers now being asked to weigh the case of Iran.

The Iraq experience has had a "sobering effect" on Iran discussions, said President Pervez Musharraf of Pakistan, a close ally of the Bush administration. In an interview, he refused to speculate on whether Iran, whose program was secretly aided by Pakistan's top nuclear scientist, had been designed for weapons production. But he said he feels confident Iran's aims are now peaceful and there was no need for Security Council action.

Iran's new president, Mahmoud Ahmadinejad, who is also attending the U.N. summit, has his own meetings scheduled in New York, and Iranian officials said he would use the gathering to mount forceful counterarguments. Iranian diplomats have been in close contact with countries such as Japan, which relies heavily on Iranian oil.

The outcome of both sides' efforts will be tested on Sept. 19, when diplomats from 35 countries meet at the International Atomic Energy Agency in Vienna to decide whether to report Iran's case to the Security Council.

Undersecretary of State R. Nicholas Burns last night suggested the administration may not be able to press for a successful vote and was exploring other options. He said the administration was working "with lots of other governments to devise an international coalition that will call upon Iran to return to the talks," it walked away from this summer with European negotiators. "There is a consensus that Iran has got to return to the talks."

Iran insists its nuclear efforts are aimed at producing nuclear energy, not bombs. The Bush administration contends that the energy program, built in secret and exposed in 2002, is just a cover. "They cannot be allowed to develop nuclear weapons under the guise of a civilian nuclear program, which is what they're trying to do," State Department spokesman Sean McCormack said earlier this month.

A recent U.S. intelligence estimate found that Iran, mostly through its energy program, is acquiring and mastering technologies that could also be used for bomb-making. But there is no proof that such diversion has occurred, the estimate said, and the intelligence community is uncertain as to whether Iran's ruling clerics have made a decision to go forward with a nuclear weapons program.

The estimate judged Iran to be as much as a decade away from being able to manufacture the fissile material necessary for a nuclear explosion. A report issued last week by the International Institute for Security Studies, a London-based research group, found Iran was 10 to 15 years from the technical know-how to build a bomb.

Both reports are based in large part on the findings of U.N. nuclear inspectors, now in their third year of investigating Iran's program. While no proof of a weapons program has been found, serious questions about Tehran's past work on centrifuge designs and experiments with plutonium -- a key ingredient for a nuclear weapon -- have yet to be adequately addressed and have furthered suspicions that the country is hiding information.

With little new information from the probe, the Bush administration put together its own presentation of Iran's program for diplomats in Vienna who are weighing whether to report Iran to the Security Council.

The presentation has not been vetted through standard U.S. intelligence channels because it does not include secret material. One U.S. official involved in the briefing said the intelligence community had nothing to do with the presentation and "probably would have disavowed some of it because it draws conclusions that aren't strictly supported by the facts."

The presentation, conducted in a conference room at the U.S. mission in Vienna, includes a pictorial comparison of Iranian facilities and missiles with photos of similar-looking items in North Korea and Pakistan, according to a copy of the slides handed out to diplomats. Pakistan largely supplied Iran with its nuclear infrastructure but, as a key U.S. ally, it is identified in the presentation only as "another country."

Corey Hinderstein, a nuclear analyst with the Institute for Science and International Security, said the presence of a weapons program could not be established through such comparisons. She noted that North Korea's missile wasn't designed for nuclear weapons so comparing it to an Iranian missile that also wasn't designed to carry a nuclear payload "doesn't make sense."